I think I understand what you are up against now, and will try to answer your questions as best I can. I can't help with identification of parts, maybe someone who has done this can.
1. Does this have to be zig/zag? No
2. Can I swap and make straight? Probably. From the picture it looks like they are both on the same level. One is the low point drain, the other is the feed to the pump. If one is lower than the other, it probably won't make much difference, but the higher one won't have access to all the water in the tank. I'd prefer the drain have the lowest one, but probably not critical.
As an aside, my low point drain started leaking. The valve was offset about 1/2" and was connected to the drain with clear plastic tubing. It was original and finally got hard and cracked. Luckily neither the tank or the drain valve was damaged.
Regarding the foam, get some larger pieces and put them on all sides of the tank in the pan so it can't move.
"You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins